#include <stdio.h>
#include <fcntl.h>
main(int args, char *argv[])
{int fdr,fdw,n_byt,i=0,status;
 char symbols[40], c;
 if ( fork())
   { wait ( & status);
     if ( open ( "file_second", O_RDONLY) != -1)
       write(1,"\n",1);
        execlp("grep", "grep","234","file_second",0);
        execlp("wc", "wc","-l","file_second",0);
    }
else { if (( fdr=open("file_first.txt",O_RDONLY))== -1)
      {printf("\n Cannot open \n"); exit(1); }
       if (( fdw=open("file_second",O_CREAT|O_TRUNC|O_RDWR,0666))== -1)
      {printf("\n Cannot open \n"); exit(1); }
     n_byt=read( fdr, symbols,22);
     write( fdw,"12345\n",6);
    c=symbols[i++];
    if ( c>='0' && c <='9')
      {  while (symbols[i++] != '\n' && i<n_byt)
                write(fdw, "12345",5);
       write(fdw,"\n",1);
       write(1,"AAA\n",4);
      }
    else {write(1, symbols,n_byt); 
          write(fdw, symbols,8);
           write(1,"\n",1);
         }
       write(fdw,"AAA\n",4);
       write(1,symbols,12);
       close(fdr); close(fdw);
    }
}

file_first.txt

123456789
AABBCCDDE